use std::cmp::{max, min};
use std::io::*;

#[test]
fn copy_copies() {
    let mut r = repeat(0).take(4);
    let mut w = sink();
    assert_eq!(copy(&mut r, &mut w).unwrap(), 4);

    let mut r = repeat(0).take(1 << 17);
    assert_eq!(
        copy(&mut r as &mut dyn Read, &mut w as &mut dyn Write).unwrap(),
        1 << 17
    );
}

struct ShortReader {
    cap: usize,
    read_size: usize,
    observed_buffer: usize,
}

impl Read for ShortReader {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let bytes = min(self.cap, self.read_size);
        self.cap -= bytes;
        self.observed_buffer = max(self.observed_buffer, buf.len());
        Ok(bytes)
    }
}

struct WriteObserver {
    observed_buffer: usize,
}

impl Write for WriteObserver {
    fn write(&mut self, buf: &[u8]) -> Result<usize> {
        self.observed_buffer = max(self.observed_buffer, buf.len());
        Ok(buf.len())
    }

    fn flush(&mut self) -> Result<()> {
        Ok(())
    }
}

#[test]
fn copy_specializes_bufwriter() {
    let cap = 117 * 1024;
    let buf_sz = 16 * 1024;
    let mut r = ShortReader {
        cap,
        observed_buffer: 0,
        read_size: 1337,
    };
    let mut w = BufWriter::with_capacity(buf_sz, WriteObserver { observed_buffer: 0 });
    assert_eq!(
        copy(&mut r, &mut w).unwrap(),
        cap as u64,
        "expected the whole capacity to be copied"
    );
    assert_eq!(
        r.observed_buffer, buf_sz,
        "expected a large buffer to be provided to the reader"
    );
}

#[test]
fn copy_specializes_bufreader() {
    let mut source = vec![0; 768 * 1024];
    source[1] = 42;
    let mut buffered = BufReader::with_capacity(256 * 1024, Cursor::new(&mut source));

    let mut sink = Vec::new();
    assert_eq!(
        std::io::copy(&mut buffered, &mut sink).unwrap(),
        source.len() as u64
    );
    assert_eq!(source.as_slice(), sink.as_slice());

    let buf_sz = 71 * 1024;

    let mut buffered = BufReader::with_capacity(buf_sz, Cursor::new(&mut source));
    let mut sink = WriteObserver { observed_buffer: 0 };
    assert_eq!(
        std::io::copy(&mut buffered, &mut sink).unwrap(),
        source.len() as u64
    );
    assert_eq!(
        sink.observed_buffer, buf_sz,
        "expected a large buffer to be provided to the writer"
    );
}
